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Home , Brine, Ion exchange

FWRJ Exchange and Disposal Issues Associated With the Waste Stream

Julie Karleskint, Daniel Schmidt, Robert Anderson, Jayson Page, and A.J. Berndt

he City of Arcadia recently completed from the local supply authority, it was Julie Karleskint, P.E., is a senior construction of a new 1.5-mil-gal-per- determined that would be the associate with Hazen and Sawyer in Tday (mgd) water treatment plant most cost-effective option for construction. A Sarasota. Daniel Schmidt, P.E., is a (WTP) using ion exchange technology to re- reduction in capacity was also provided since senior associate with Hazen and Sawyer place its 3-mgd WTP. The lime the City’s water supply source, in Tampa. Robert Anderson, P.E., is a plant had reached the end of its serviceable life from the intermediate aquifer, was limited senior associate with Hazen and Sawyer and the treatment of groundwater for the re- based on current pumping limitations and in Orlando. Jayson Page, P.E., is a moval of radionuclides, hardness, sulfides, or- permitted capacity. senior associate with Hazen and Sawyer ganic carbon, and was desired in The groundwater is supplied from six order to provide safe drinking water to the , approximately 350 ft deep and located in Coral Gables. A.J. Berndt is the utility community. After evaluating several treatment within a 1-mi radius of the plant. A summary director for the City of Arcadia. technologies, including lime treatment, of the water quality from the wellfield is shown , ion exchange, and purchases in Table 1. In reviewing the groundwater quality, re- Table 1. Arcadia Groundwater Quality duction in radium 226 and gross alpha is nec- essary to meet primary drinking water standards. Reduction in fluoride, sulfide, total organic carbon (TOC) and hardness is also de- sired to meet secondary standards and reduce the demands caused by the presence of sulfides and TOC, as as minimize the formation of disinfection byproducts. The use of ion exchange was determined to be the most cost-effective treatment for ra- dionuclides. Cation exchange is commonly used for the removal of radionuclides and hardness. Anion exchange could also be pro- vided for the removal of sulfides, organic car- bon, and possibly, some fluoride. However, since ion exchange can utilize a significant amount of in its process and during re- generation, there were concerns as to how much salt would be added to the system based upon the amount of water treated. In order to develop a better understand- ing of the process, pilot testing was performed. The test results could then be used to deter- mine the effectiveness of the anion and cation exchange resins, blending requirements, run- Table 2. Maximum Contaminant Level and Target Reduction time lengths, headloss, and brine regeneration requirements. In setting up the pilot test, max- imum contaminant levels (MCLs) and target concentrations for the WTP were developed, as shown in Table 2. The objectives of the pilot study were to examine the ability of the cation exchange system to consistently achieve soft- ening and radium removal. It was also to ex- the ability of the anion exchange system to adequately remove sulfide and total organic carbon, with the addition of aeration to bio-

56 April 2014 • Florida Journal logically promote the conversion of sulfide to sulfate. The pilot equipment consisted of a re- duced-scale ion exchange testing apparatus provided and assembled by Tonka Equipment Company, as shown in Figure 2. The study was conducted over a 30-day period, with approx- imately six hours of runtime each day. The de- sired flow rate and runtime for the cation exchange column was 6.5 gal per hour (gph) for 24 hours, resulting in 160 gal of treated water. The anion exchange column desired flow rate and runtime was 8.1 gph for 65 hours, yielding 525 gal of treated water. Two complete brine regenerations were performed prior to the first run in order to ensure that the resin was in a chloride form. To simulate the designed full-scale soft- ening cation exchange vessel, an 8-ft-tall, 2-in.- diameter column was filled to a depth of 60 in. with Thermax T-42 Na high-capacity strong acid resin. A gage and pressure reducing valve were provided on the inlet line to monitor and control column pressure. Headloss was meas- ured by an additional gage connected between the columns influent and effluent lines. Rate of flow control and a flow meter were plumbed into the column’s discharge so as to maintain a constant treatment flow rate. Figure 1. Pilot Test Equipment Similarly, a full-scale anion exchange ves- sel, with a 5-ft-tall, 2-in.-diameter column was filled to a depth of 36 in. with Thermax A-72 Table 3. Anticipated Water Quality From Water Treatment Plant MP high-capacity strong base resin. A gage and pressure reducing valve was provided on the inlet line to monitor and control column pressure. Headloss was measured by an addi- tional gage connected between the column’s inlet and discharge lines. Rate of flow control and flow meter are plumbed to the column’s discharge so as to maintain a constant treat- ment flow rate. The testing apparatus was set up accord- ing to the pilot test protocol. The blended water was then aerated with .05 cu ft per hour (cfh) of air. The oxygen is used to help main- Using the data obtained by the pilot test- plant still needed to be evaluated. tain conditions that are favorable to bacteria ing, it was determined that if 40 percent of the The City’s wastewater plant is a 2-mgd that can biologically oxidize the sulfide. The groundwater could be bypassed around the plant with high-level disinfec- flow then passes through the anion exchange cation exchange system and recombined prior tion to provide public access reuse. The plant column where sulfide and organics are re- to the anion exchange system, all the water or provides to orange groves, a duced. The anion exchange column received percentage thereof could then receive treat- golf course, cemetery, parks, and residential and processed all of the 6.5 gph of blended ment through the anion exchange columns. customers, with a backup surface water dis- water, simulating the conditions of the full- This would result in significantly reduced sul- charge for wet weather. High concentrations scale process. Based on the pilot testing results, fide and TOC concentration, which would re- of salt in can be problematic, it was confirmed that significantly longer run- sult in a lower chlorine demand. Using a blend since salt can reduce crop productivity. This is times could be achieved by providing an envi- of 60 percent cation and 100 percent anion, it primarily caused by less water being available ronment conducive to the biological oxidation was estimated that approximately 1,800 lbs of to the plant due to competing . High salt of sulfides. Based on these results, the esti- salt would be required to treat 1 mil gal (MG) concentrations can also cause to become mated salt usage was determined to be signif- of water. The resulting anticipated water qual- sodic, resulting in a degraded structure, icantly less than originally assumed for the ity would meet regulatory standards and the which can prevent the plant from absorbing anion units, while still achieving the water city’s water quality objectives, shown in Table the water. Therefore, the amount of salt that quality goals. 3. However, the impact on the wastewater Continurd on page 58

Florida Water Resources Journal • April 2014 57 Figure 2. New Arcadia Ion Exchange Water Treatment Plant

Continurd from page 57 dicted concentrations ranged from DeSoto County to assist in reducing flushing would be added to the wastewater plant as a 100 mg to 170 mg/L and the predicted chlo- and maintaining flow in its system. result of the ion exchange process was a sig- ride levels ranged from 130 mg/L to 260 mg/L. The water produced from the plant is nificant concern. In reviewing the anticipated water qual- currently meeting all water quality standards, Although, the discharge of the ion ex- ity, it was noted that the average sodium and treating 60 percent of the water through the change waste stream is not specifically regu- chloride concentrations would meet the water cation system and 100 percent through the lated by the Florida Department of quality standards of 160 mg/l sodium and 250 anion system followed by disinfection, storage, Environmental Protection (FDEP), since it is mg/l chloride. In addition to the sodium and and high-service pumping. Additional treat- not considered as an industrial waste, the re- chloride concentrations, the sodium adsorp- ment with caustic soda for pH adjustment, quirements for the blending of demineraliza- tion ratio (SAR) was also evaluated. The SAR and for stabilization and corrosion control, is tion concentrate with reclaimed water were is a measure of the suitability of water for use provided; however, minimal usage is required. evaluated. The FDEP Rule 62-610.875 (13) in agriculture based on concentrations of The ion exchange regenerate waste from FAC, Blending of Demineralization Concen- solids dissolved in the water, which is calcu- the regeneration cycles is stored in tanks and trate with Reclaimed Water, indicates that the lated as follows: slowly pumped to the wastewater collection addition of concentrate shall not impair the system at a rate of approximately 50 gal per ability of the treatment facility to meet re- SAR = [Na+] / {([Ca2+] + [Mg2+]) / 2}1/2 min (gpm). Recent testing shows that the im- claimed water limitations, or harm vegetation pact on the wastewater system has not been grown in the reuse system. It also indicates Waters with SAR >6 can cause negative significant and agriculture reuse customers that the reuse system must comply with impact to vegetation by limiting of have not been negatively impacted. Conduc- groundwater standards at the edge of the zone water through soil. The SAR based on the pro- tivity monitoring at the WWTP has indicated of discharge. Therefore, these factors were posed water quality was determined to be 4.5, that the concentration of evaluated to verify that the discharge of the which was less than 6 and therefore should not (TDS) after a regeneration cycle ranges be- brine waste would be acceptable to the re- negatively impact the agricultural reclaimed tween 200 mg/l to 500 mg/L, which is similar claimed water system. water users. to what was anticipated. A review of the In evaluating the impact of the salt on the Based on the pilot test results and pre- groundwater monitoring results for the reuse wastewater plant, the amount of salt being liminary engineering study, it was determined areas for the past year also shows no signifi- added to the system and the historical sodium that the disposal of the brine would not cause cant increases in sodium or chloride in the and chloride concentrations of the wastewater any significant issues to the wastewater plant. groundwater. The City will continue to mon- effluent were evaluated. This analysis showed Therefore, the City commenced construction itor the wastewater and groundwater quality that the sodium and chloride values in the ef- on the new 1.5-mgd ion exchange WTP in Jan- as production from the WTP increases. fluent varied based on season, with sodium uary 2012. The new plant (Figure 2) was re- and chloride concentrations being higher dur- cently completed, with water production ing the dry seasons. This data was then used to initiating in January 2013. The plant is cur- predict sodium and chloride concentrations rently producing approximately 0.7 mgd, since for the treated wastewater effluent. The pre- the facility is also accepting treated water from

58 April 2014 • Florida Water Resources Journal